In a conventional load electromyogram used for measurement of fatigue by an electromygram, the load often has a constant value. For example, an experiment on arm bending utilizing an ergometer was an experiment on the fatigue resulting from repeated movements of raising a weighted body to a definite position, and not an experiment about the muscular strength and the electromyogram in the process of reaching the maximum muscular strength. It was also impossible to know whether or not the subject is already tired or feels pain at the time of measurement and, if he is tired or feels pain, what its degree is.
The inventor reported a method of recording the discharge amount derived from a muscle being tested and the muscular strength of the muscle being tested as a muscular strength electromyogram on a recorder by passing the discharge amount through an input means and further an electromyogram amplifier on the one hand, and by passing the muscular strength through a transducer to convert it into an electric signal which is supplied to an amplifier on the other hand, the muscular strength and electromyogrammatic signals from these amplifiers being supplied to a recorder amplifier and then to the recorder ("Industrial Medicine," Vol. 18, No. 4, 1976, pp. 383 to 390). It has been found from the muscular strength electromyogram obtained by this method that the amplitude of the electromyogram increases as the muscular strength increases and the discharge amount of the muscle at the time of fatigue is higher than that when not tired. It has also been found that when the muscle is dead tired, the discharge amount increases considerably in spite of reduced muscular strength. However, there is a problem to this method that the degrees of fatigue cannot be exactly compared numerically.
Also the inventor has found it necessary to find the areas of muscular strength electromyograms to obtain the ratio therebetween in order to exactly compare the degrees of fatigue of muscles based on the muscular strength electromyograms and reported a method of measuring and comparing the areas of electromyograms ("Industrial Medicine," Vol. 20, No. 2, 1978, pp. 94 to 104). According to this method, the areas of electromyograms can be found by forming the envelopes thereof as shown in FIG. 9. However, this method has the disadvantage that not only is there a considerable error in drawing envelopes due to differences of individuals, but also it is a time consuming and troublesome work to obtain the envelopes.
To overcome these shortcomings it was necessary to find the ratio between the integrals of the muscular strength and the electromyogram to display it.
On the other hand, the muscular strength depends on the constitution or physique of the individual. The extent of the constitution can be represented by the body weight. Since a person of a lighter weight is lower in the muscular strength than a person of a heavier weight, the ratio between the integrated values of the electromyogrammatic amplitude to muscular strength is smaller even though the integrated values of the electromyogrammatic amplitudes are the same. This fact suggests that the numerical values of subjects of different weights cannot be compared as they are.
The present invention has overcome these difficulties.